Power clamps are used in automotive and other industries for clamping together two workpieces, for example, while they are being welded. Pneumatic, hydraulic and electrically powered clamps have been used. The electric clamps produce no exhaust fumes, contamination, loud noise, nor leakage, and require no plumbing or seals. An example is described in U.S. Pat. No. 4,723,767, Appl. No. 894,963, Filed Aug. 8, 1986, issued Feb. 9, 1988, of inventor Alexander W. McPherson, which is incorporated herein by reference. It is a rotary-powered, linearly-actuated clamp having a hollow electric motor drive shaft coupled to rotate a threaded nut. The nut is axially retained by reaction roller thrust bearings to enable it to drive a linear threaded rod. The rod has an integral toggle linkage actuator, guided by anti-friction rollers in linear reaction tracks.